Abstract The current opioid crisis has resulted in increases in opioid use and abuse during pregnancy that parallel national trends of substance use. Between 2000 and 2012, the incidence of maternal opioid use during pregnancy increased from 1.19 to 5.77 per 1000 hospital live births per year. Maternal opioid use during pregnancy is associated with increased risks of prolonged hospital stay, maternal death, placental abruption, poor fetal growth, preterm labor, premature delivery, and stillbirth. Maternal opioid use can also result in neonatal abstinence syndrome (NAS), an opioid withdrawal condition occurring in 55-94% of infants whose mothers used opioids in pregnancy, the incidence of which has increased over the past decade. Opioid prescribing practices, rates of opioid use in pregnancy, and incidence of NAS vary substantially between states, suggesting that state policies may affect maternal, fetal, and neonatal outcomes. Indeed, state responses regarding treatment of opioid use disorders in pregnancy have varied widely and included creation of funded drug-treatment programs specifically for pregnant women, priority access to state-funded treatment programs, mandated reporting and drug screening by healthcare professionals, and criminalization of the behavior with grounds for commitment. While a public health response to the opioid epidemic has been proposed in favor of punitive action, evidenced-based data about what specific public health strategies result in the best outcomes for opioid-using mothers and their infants are limited. We propose to use two large, national databases to better understand the effects of these state policies on the prevalence of OUD in pregnant women, as well as patterns of prenatal and OUD care utilization, pregnancy complications and adverse outcomes, and costs. By using data from the MarketScan Commercial Claims and Encounters and the Medicaid Analytic eXtract (MAX) files, this study will provide a comprehensive assessment of the effects of these policies on maternal and neonatal outcomes in pregnant women with OUD. This proposal, responsive to AHRQ?s Special Emphasis Notice (NOT-HS-18-015) calling for research to evaluate ?state, local, and health system policy efforts to address the opioids crisis,? will address the following aims: 1) Examine the effects of state policies governing the treatment of pregnant women with OUD on the prevalence of OUD in pregnant women; 2) Examine the effects of state policies on patterns of treatment and costs, both for prenatal care and OUD treatment, for pregnant women with OUD; and 3) Examine the effects of state policies on maternal and child outcomes and costs for pregnant women with OUD. This study will take advantage of a unique set of databases that will allow for a comprehensive examination of the effects of state policies on treatment patterns and maternal and neonatal outcomes for pregnant women with OUD. The information generated from the study will be crucial to providers, insurers and policymakers as they design treatment processes and policies to provide adequate pregnancy and OUD care to this vulnerable population.